Map of the spruce genome and tandemly arrayed genes. The 12 spruce chromosomes were plotted with Circos . From inside to outside: gene-rich regions in red; the 12 chromosomes with ticks representing the genes mapped along the spruce linkage groups, and with genetic distances in cM (Kosambi); distribution of the tandemly arrayed genes. The chromosome nomenclature and numbers of genes mapped are inside the circle. For the complete names of tandemly arrayed genes, see Additional file 4.